I assume this is a shared resource somewhere in Windows. Rather than making a copy for each app, is there a way to use this icon just like all Winforms apps use it?
If you have Visual Studio 2010 installed then there is a large collection of icons (potentially including the application icon/s), check out the following directory:
%ProgramFiles%\Microsoft Visual Studio 10.0\Common7\VS2010ImageLibrary\1033
There may be a similar directory for previous VS versions, take a look if needs be.
EDIT:
On doing a search in the folder of the unzipped file for app there are two notable results:
Application.ico and ApplicationGeneric.ico + its *.png counterpart.
If you have VS 2010 and any of the icons in here are suitable, I believe you don't need to copy a single one - you should be able to include the file indirectly (as a shared/linked file) when adding using the Existing Item... dialog; you do this by selecting the arrow next to Add button and selecting the Add As Link option.
What I can't see working as desired is simply overwriting these files in an attempt to apply a global change.